4.2 Modbus Basic functions Modbus uses a master-slave technique in which only the master can initiate
a transaction. The slaves respond by supplying the requested data in a reply
or by executing the action requested in the query.
The Modbus telegram from the master contains the slave address, a func
-
tion code defining the requested action, a data field, and a CRC field. The
Modbus slaves’ response message contains fields confirming the requested
action and possibly the requested data and also a CRC field.
If an error occurs during reception of the telegram or the slave is unable to
perform the requested action, the slave will generate an error telegram and
send it as response to the master.
4.3 Transfer mode
.
RS-485 twisted pair cable or fibre optic cable.
.
AUMA actuators support baud rates up to 38.4 kBit/s
4.4 Bus access
.
Master-slave technique.
.
Mono-master system.
.
Master and slave devices: max. 127 devices at one bus
(the AUMA MATIC supports slave addresses from 1 to 127), without
repeater max. 32 devices.
4.5 Communication
.
Master-slave data exchange via query-response cycle (Polling procedure).
.
Modbus RTU protocol.
4.6 Protection functions
.
Parity check for each telegram byte
.
CRC check for each telegram
.
Watchdog for AUMA actuators with adjustable failure behaviour.
.
Query-response cycle monitoring with configurable timer interval at the
master.
4.7 Modbus RTU mode Data format for a byte.
Coding system:
.
8 bit binary, hexadecimal 0-9, A-F
.
2 hexadecimal characters contained in each 8 bit field of the telegram
Bits per byte:
.
1 start bit
.
8 data bits; least significant bit sent first
.
1 bit for even/ odd parity, no bit for no parity
.
1 stop bit if parity is used, 2 stop bits if no parity is used.
6
Actuator controls AUMA MATIC AM/ AMExB/ AMExC
Modbus Operation instructions
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